RuBP Regeneration Dependent and Electron Transport Limiting Rate Aj

A continuous rate of C02 reduction or oxygenation activity requires continuous and equal rate of RuBP supply. RuBP is regenerated via the pentose phosphate cycle or the photorespiratory C-oxidation cycle. Both processes consume ATP and NADPH and there is a very complex stoichio-metry, i.e. PGA (phosphoglycerate) production, the rate of NADPH and ATP consumption, and the number of electrons required to produce the redox equivalents and ATP. This is in turn dependent on the linear rate of electron transport through PS I and PS II as well as on cyclic electron transport. The sum of these processes is:

where J' is the maximum carboxylation rate maintaining the potential rate of electron transport and J is the potential rate of linear electron transport. It follows that the Rubisco limiting rate of C02 assimilation, Aj, is:

where J is the rate of electron transport. J increases hyperbolically with light (Q):

where 9 describes the curvature of the hyperbolic function. Vcmax depends, as with Jmax, on temperature and other growth conditions. In practice the temperature dependence of Vcmax and Jmax is experimentally determined from a regression of the dependence of photosynthesis on conductance, measured experimentally under the climatic conditions of interest.

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